And if you are looking for teacher's editions for homeschooling purposes, inquire with some professors at your local community college. My wife recently brought home 100+ volumes in various subjects from her college here in Nevada. The professors get new editions constantly and the old ones generally are thrown away. Jess (my wife) was collecting them for a group that supplies books to schools in Africa. We went through and picked out a dozen to add to our homeschooling library or to replace editions we no longer wanted.